Process for producing polyolefins and polyolefin catalyst

Abstract

The present invention provides a process for preparing polyolefins having a multimodal or at least bimodal molecular weight distribution by contacting in a reaction mixture under polymerization conditions at least one olefin and a catalyst system comprising a supported catalyst-component comprising an alumoxane and at least two metallocenes containing the same transition metal and selected from mono, di, and tri-cyclopentadienyls and substituted cyclopentadienyls of a transition metal and wherein at least one of the metallocenes is bridged and at least one of the metallocenes is unbridged.

We claim: 
     
       1. A process for the preparation of polyolefins having a multimodal or at least bimodal molecular weight distribution comprising: (1) providing a catalyst system comprising (a) a supported catalyst-component comprising an alumoxane and at least two supported metallocenes effective for olefin polymerization containing the same transition metal and selected from the group consisting of mono, di- and tri-cyclopentadienyls and substituted cyclopentadienyls of a group 4b, 5b or 6b transition metal wherein at least one of the supported metallocenes is bridged and at least one of the supported metallocenes is unbridged with the molar ratio of said unbridged to bridged metallocenes in said catalyst system being within the range of 4:1 and 2:1 and (b) a cocatalyst;   (2) contacting said catalyst system in a polymerization reaction zone with at least one olefin and maintaining said reaction zone under polymerization conditions to produce multimodal or at least bimodal molecular weight distribution polymer of said olefin.   
     
     
       2. The process according to claim 1 wherein the catalyst system comprises one or more cocatalyst represented by the formula MR x  wherein M is a metal selected from the group consisting of Al, B, Zn, Li and Mg, each R is the same or different and is selected from the group consisting of halides, and alkoxy or alkyl groups having from 1 to 12 carbon atoms and x is from 1 to 3. 
     
     
       3. The process according to claim 2 wherein the cocatalyst is a trialkylaluminium selected from the group consisting of trimethylaluminium, triethylaluminium, triisobutylaluminium, tri-n-hexylaluminium and tri-n-octylaluminium. 
     
     
       4. The process of claim 3, wherein said metallocenes contain a transition metal selected from the group consisting of titanium, zirconium, hafnium and vanadium. 
     
     
       5. The process according to claim 1 wherein the polymerization reaction is run in a diluent selected from the group consisting of isobutane, n-hexane, n-heptane, methylcyclohexane, n-pentane, n-butane, n-decane, and cyclohexane. 
     
     
       6. The process according to claims 1 wherein hydrogen is introduced into the polymerization reaction zone in an amount ranging from about 0.001 to 15 mole percent hydrogen based on total hydrogen and olefin present. 
     
     
       7. The process according to claims 1 wherein the unbridged metallocenes are represented by the formula (Cp) 2  MX 2  wherein each Cp is the same or different and is selected from the group consisting of substituted and unsubstituted cyclopentadienyl, indenyl or fluorenyl, M is zirconium, titanium or hafnium and X, which is the same or different, is a hydrocarbyl radical selected from the group consisting of aryl, alkyl, alkenyl, alkylaryl, and aryl alkyl radical having from 1-20 carbon atoms and a halogen;   the bridged metallocenes are represented by the formula R"(Cp) 2  MX 2  wherein each Cp is the same or different and is selected from the group consisting of substituted and unsubstituted cyclopentadienyl, indenyl and fluorenyl, M is zirconium, titanium or hafnium and X, which is the same or different, is a hydrocarbyl radical selected from the group consisting of aryl, alkyl, alkenyl, alkylaryl, and aryl alkyl radical having from 1-20 carbon atoms or a halogen and R" is a C 1  -C 4  alkylene radical, a dialkyl germanium or silicon or siloxane, or an alkyl phosphine or amine radical bridging two (Cp) rings.   
     
     
       8. The process according to claim 7 wherein, in the formula of the unbridged metallocene, Cp is a substituted or unsubstituted cyclopentadienyl or indenyl, M is zirconium, titanium or hafnium and X is Cl or CH 3 , and in the formula of the bridged metallocene Cp is a substituted or unsubstituted cyclopentadienyl, indenyl or fluorenyl, M is zirconium, titanium or hafnium, X is Cl or CH 3  and R" is an ethylene radical or dialkyl silicon. 
     
     
       9. The process according to claim 8 wherein the unbridged metallocene is a bis(cyclopentadienyl) zirconium dichloride and the bridged metallocene is an ethylene-bis(indenyl) zirconium dichloride. 
     
     
       10. The process of claim 1, wherein said supported catalyst component comprises said two metallocenes collectively supported on the same support. 
     
     
       11. The process of claim 10, wherein said supported catalyst component is prepared by adding a solution of the two metallocenes to the same support. 
     
     
       12. The process of claim 11, wherein said alumoxane is added to said support prior to said metallocenes. 
     
     
       13. The process of claim 1, wherein said bridged metallocene is deposited on a first support and a unbridged metallocene is deposited on a second support followed by mixing the two separately supported metallocenes together. 
     
     
       14. The process of claim 13, wherein said alumoxane is added to said supports prior to the deposition of said metallocenes on said supports. 
     
     
       15. In a process for the preparation of polyolefins having a multimodal or at least bimodal molecular weight distribution, the steps comprising (1) providing a catalyst system comprising (a) a finely divided support material containing an alumoxane and at least two metallocenes effective for olefin polymerization supported on said support material, said metallocenes containing the same transition metal and selected from the group consisting of mono, di- and tri-cyclopentadienyls and substituted cyclopentadienyls of a group 4b, 5b or 6b transition metal wherein at least one of the supported metallocenes is bridged and at least one of the supported metallocenes is unbridged and the molar ratio of said unbridged to bridged metallocenes in said catalyst system being within the range of 4:1 and 2:1;   (2) providing a cocatalyst; and   (3) contacting said catalyst system in a polymerization reaction zone with at least one olefin and maintaining said reaction zone under polymerization conditions to produce multimodal or at least bimodal molecular weight distribution polymer of said olefin.   
     
     
       16. The process of claim 15 wherein said supported catalyst component is prepared by adding a solution of the two metallocenes to said support material. 
     
     
       17. In a process for the preparation of polyolefins having a multimodal or at least bimodal molecular weight distribution comprising the steps of: (1) providing a catalyst system comprising at least two supported metallocenes effective for olefin polymerization and containing the same transition metal and selected from the group consisting of mono, di- and tri-cyclopentadienyls and substituted cyclopentadienyls of a group 4b, 5b or 6b transition metal wherein at least one of the supported metallocenes is bridged and at least one of the supported metallocenes is unbridged, said bridged metallocene being deposited on a first finely divided support material and said unbridged metallocene being deposited on a second finely divided support material which is in admixture with said first support material;   (2) providing a cocatalyst; and   (3) contacting said catalyst system in a polymerization reaction zone with at least one olefin and maintaining said reaction zone under polymerization conditions to produce multimodal or at least bimodal molecular weight distribution polymer of said olefin.   
     
     
       18. The process of claim 17 wherein the molar ratio of said unbridged to bridged metallocenes in said catalyst system is within the range of 4:1 and 2:1. 
     
     
       19. In a process for the preparation of polyolefins having a multimodal or at least bimodal molecular weight distribution, the steps comprising: (1) providing a finely divided support material containing an alumoxane;   (2) contacting said support material with a mixture of at least two metallocenes effective for olefin polymerization containing the same transition metal and selected from the group consisting of mono, di- and tri-cyclopentadienyls and substituted cyclopentadienyls of a group 4b, 5b or 6b transition metal wherein at least one of the metallocenes is bridged and at least one of the metallocenes is unbridged to produce a catalyst system;   (3) providing a cocatalyst; and   (4) contacting said catalyst system and cocatalyst in a polymerization reaction zone with at least one olefin and maintaining said reaction zone under polymerization conditions to produce multimodal or at least bimodal molecular weight distribution polymer of said olefin.   
     
     
       20. In a process for the preparation of polyolefins having a multimodal or at least bimodal molecular weight distribution, the steps comprising: (1) providing a first finely divided support material containing an alumoxane;   (2) contacting said support material with a bridged metallocene effective for olefin polymerization selected from the group consisting of di- and tri-cyclopentadienyls and substituted cyclopentadienyls of a group 4b, 5b or 6b transition metal;   (3) providing a second finely divided support material containing an alumoxane;   (4) contacting said second support material with an unbridged metallocene effective for olefin polymerization containing the same transition metal and selected from the group consisting of mono, di- and tri-cyclopentadienyls and substituted cyclopentadienyls of a group 4b, 5b or 6b transition metal which is the same transition metal as in said bridged metallocene;   (5) mixing the products of steps 2 and 4 together to provide a catalyst system;   (6) providing a cocatalyst; and   (7) contacting said catalyst system and cocatalyst in a polymerization reaction zone with at least one olefin and maintaining said reaction zone under polymerization conditions to produce multimodal or at least bimodal molecular weight distribution polymer of said olefin.